update changelog for 0.4.0

[incanus]

It's always easy to do an initial release! Now we have to update this guy and I could use some help.

Let's work at https://gist.github.com/incanus/051c2bfc5057ae414e6a until we're happy, then plop it into the live one.

Or just paste ideas/remembrances here.

@mapbox/gl

[1ec5]

• MGLMapView no longer manages Mapbox access tokens directly; an access token cannot be passed in when initializing the map view. Instead, set MGLMapboxAccessToken to your access token in your app’s Info.plist file, or call +[MGLAccountManager setAccessToken:] before initializing the map view. If you were setting the access token inside an Interface Builder inspectable, also remove it from the User Defined Runtime Attributes section of the Identity inspector. (Grab app-wide data from Info.plist #1553)
• -[MGLAccountManager setMapboxMetricsEnabledSettingShownInApp:] has been removed. If you implement a Mapbox Metrics switch inside your app, instead of inside a Settings bundle, set MGLMapboxMetricsEnabledSettingShownInApp to YES in the Info.plist file. (Grab app-wide data from Info.plist #1553)
• MGLMapView supports Interface Builder designables. When you add an MGLMapView to a storyboard, it displays instructions for getting set up directly on the storyboard canvas. (Restore IB designable support #1573)
• Headers have been audited for nullability, improving type safety in both Objective-C and Swift 1.2 when compiling with Xcode 6.3 or above. (Audit headers for nullability #1578)
• Headers now make use of lightweight generics, eliminating many unnecessary casts when working with annotations in Swift 2.0 in Xcode 7. (Adopt lightweight generics #1711)
• -[MGLMapView mapID] has been renamed -styleID. (mapID → styleID #1561)
• The default title for the user location annotation is now “You Are Here”. You can customize the title by setting mapView.userAnnotation.title. (Less bland default title for user dot annotation #1559)
• Internal use of the Reachability library has been cleaned up so that your app can include its own copy of Reachability. (Namespace Reachability notification constant #1718)

[jfirebaugh]

I believe that all my changes were internal-only and probably not interesting for a changelog beyond a general "improve overall performance and stability" item.

[1ec5]

• Improved placement and density of labels. (port labeling, symbol sorting, and reparsing overscaled tiles #1666)
• Added a shortcut to the Mapbox Metrics switch to the action sheet that is attached to the ℹ️ button. ([squash] Add action sheet shortcut to Settings.app metrics opt-out #1611)
• Fixed an issue in which certain features, such as roundabouts, were not rendered completely. (fix roundabout not closed #1725)
• Fixed an issue in which the map would sometimes spin 180° while rotating the map with two fingers. (Prevent full-circle spin during animated rotation #1453)

[1ec5]

@incanus, we don’t want to bury the lede on #1553, which is a breaking change.